docs: def stats_per_utterance(self):
          """
          Return statistics calculated for all samples of each utterance in the corpus.
  
          Returns:
              dict: A dictionary containing a DataStats object for each utt.
          """
  
          all_stats = {}
  
          for utterance in self.utterances.values():
              data = utterance.read_samples()
              all_stats[utterance.idx] = stats.DataStats(float(np.mean(data)),
                                                         float(np.var(data)),
                                                         np.min(data),
                                                         np.max(data),
                                                         data.size)
  
          return all_stats